1. Field of the Invention
The present invention relates to an auxiliary switch arrangement having at least two fixed contact pieces that are fastened inside a housing, and at least one spring-loaded contact bridge that connects or leaves disconnected the fixed contact pieces depending on the position of a slide equipped with linear cams.
2. Description of Related Art
European Patent EP-B1-0347999 which corresponds to U.S. Pat. No. 4,983,788, describes an auxiliary switch arrangement of the type mentioned above. In this auxiliary switch arrangement, two or more fixed contact pieces are arranged inside a housing. In a switched-on position, the two fixed contact pieces are connected to each other by a movable contact bridge. The contact bridge is attached as a bar on one end of a T-shaped hinge pivot swing lever, which is attached inside the housing with its other end. The swing lever is spring-loaded in the closing direction of the contact pieces by a helical spring. Inside the housing, a slide with linear cams is bearing-supported so that it can move. Generally, the slide is coupled onto an electrical switching device and is moved along with movable contact pieces of the switching device. The linear cams on the slide engage the swing levers and move them with the contact bridges against the spring action. In a switched-off position of the auxiliary switch, the cams lift the contact bridges off the fixed contact pieces. In the switched-on position, the helical spring generates the contact pressure for the contact bridge.
A primary disadvantage of this auxiliary switch arrangement is that the swing lever must be pivoted inside the housing in a hinged manner, which requires the provision of bearing supports. The assembly of the swing levers in conjunction with the helical coil makes the auxiliary switch arrangement unsuitable for automatic assembly.
U.S. Pat. No. 3,016,440 describes another similarly designed auxiliary switch arrangement which has an additional helical spring. However, the additional helical spring adds to the number of components, the assembly cost, and the actuating force which must be generated by the actuators of the electrical switching device. In addition, the additional helical spring can result in matching problems when coupling onto different switching devices with dissimilar strokes.
U.S. Pat. No. 3,675,168 describes a switching device with a fixed contact piece located inside a housing and with a movable contact piece attached to one end of a U-shaped, curved leaf spring strip. The other free end of the leaf spring strip is fastened onto the housing, and serves as an electrical connection point. The movable contact piece on one end of the leaf spring strip is engaged and disengaged with the fixed contact piece by a slide through a cam arrangement which is away from the contact point.
A primary disadvantage of this auxiliary switch arrangement is that the electro-dynamic forces that occur within the parallel parts of the U-shaped leaf spring strip, especially during an excess current, can excite oscillations and result in contact separation. In addition, the current-carrying U-shaped leaf spring strip is heated by the flowing current which, especially during excess currents, can alter the spring characteristics of the leaf spring strip.